1. Field of the Invention
The invention relates to aircraft gas turbine engine thrust-reversers. More particularly, it relates to thrust reversers which are designed with particular attention to resist impacts from objects from the gas turbine engines around which they are configured.
2. Description of the Related Art
Aircraft thrust-reversers are well known equipment to reverse the direction of flow of the propellant gas generated by the gas turbine engine powering the aircraft in order to decelerate the aircraft.
The thrust reversers are in the form of an annular structure enclosing the gas turbine engine. This annular structure comprises a first portion, i.e., a fixed structure, which includes by a plurality of radial apertures and a second portion constituted by at least one displaceable shutter or door means to close the radial apertures. When the radial apertures are closed, the propellant gas flow generated by the gas turbine engine is channeled rearward to propel the aircraft in a forward direction. When the radial apertures are open, the propellant gas flow is directed through said apertures forwardly to decelerate the aircraft.
The shutters must be kept in the closed position with high reliability. Accordingly each shutter typically is held closed by at least one main locking system and by at least one reserve or emergency locking system designed to keep the shutter closed even in the event of main locking-system malfunction. The expression "locking system" denotes a lock mounted on part of the annular structure, the lock cooperating with a lock-interface means mounted on the other part of the annular structure. Usually, but not necessarily, the lock is mounted on the fixed structure and the lock-interface means is mounted on the shutter.
Most thrust reversers may be considered to be of two types. In one type, the shutters are mounted in pivotable manner in the radial apertures. In the second type, a single annular shutter encloses the fixed thrust-reverser structure and covers the radial apertures, the aperture opening being implemented by rearwardly translating the shutter.
The annular structure of the thrust reverser is radially bounded by two thin walls or skins, namely an inner wall channeling the propellant-gas flow and an outer wall against which the ambient air flows. These walls are interconnected by bracing or frame structure to achieve a lightweight and simultaneously rigid and structurally integral thrust reverser. Typically the locking systems are mounted on the bracing means of the fixed structure and the shutters.
Inherently, the fixed structure's framing is a complex structure. It comprises a first rigid ring or fore frame, a second rigid ring or rear frame and a plurality of longitudinal beam elements rigidly joined by their ends to the fore frame and to the rear frame, the radial apertures being configured between the longitudinal beams. Moreover, thrust reversers are known which lack a rear frame, the longitudinal doors consequently being affixed by their front ends to the fore frame while their rear ends remain free.
Though quite rare, gas turbine engine accidents may seriously damage the thrust reverser. Illustratively, a rotor blade, or even a rotor disk, may rupture. Due to the centrifugal force, the fragments thereof may impact the thrust reverser.
Damage so created may be limited to more or less localized deformation of the annular thrust-reverser structure and its bracing means. Nevertheless, such deformation may render a locking system inoperative because of the ensuing gap between the lock and the lock-interface means, possibly leading to the premature opening of the shutter. Therefore, a first problem is keeping the shutters closed despite the deformation of the annular thrust-reverser structure.
More serious yet, the damage may rupture a bracing element, in particular the fore frame, a longitudinal beam or the rear frame, whereupon the thrust reverser may no longer be structurally functional. Consequently, a second problem is precluding loss of thrust-reverser structural functionality in case of bracing-means rupture.
Monitoring the proper shutter locking is based on electric detection and signaling means combined with the mechanical components controlling locking. The signaling means also may malfunction or transmit spurious locking signals. A dangerous situation may ensue, which remains undetectable when the aircraft is on the ground and ready for takeoff, when the shutters are closed but unlocked. A third problem is reliably signaling to ground that the locking systems are closed.